dave269

This cat is my first and so far had it out 3 times & I love it so far except for the porpoise between 90 and 100 mph. The mtr is a 565 blower mtr w/ 890hp and running a 34p bravo one prop. I only have trimmed it about 1/2 way & wasn't sure if I should go more or will it get worse. I'm open for suggestions, maybe the prop needs to be reworked for more stern lift ??

fast times

Tunnel tabs may help but not sure on that size of boat?

HiMark Racing

I had the same boat with same power with same issue..Today is your lucky day.. Your prop is to BIG. What RPM are you turning at 100 MPH?? I had a 32 and was turning 5000, I went to a Labbed 30 and what a difference...you blow right thru that porpoise..

Naughty Kitty

All cats hop. As the air packs the tunnel and lifts the hull, the vent in the back opens larger and drops the pressure. Boat falls back in the soup until the air pack lifts it again. The conditions and trim (combined with HP to push it) all have a influencing effect on this. Best way to contradict the effect is tunnel tabs, but if your willing to try different props and trim angles you can learn the right balance to mitigate the effects of venting.

dave269

going to try the 32 again this weekend, I just installed a tach memory box , still a little nervous about looking at gauges @ 100 mph. Last time I ran the 32 a guy from shore said it sounded like I hit the rev limiter, I didn't hear it but prob wouldn't over wind & blower whine. should have a better answer sunday on the rpms

the deep

iTrader: (8)

Dave , don't trim it any farther than 90* with the tunnels and maybe a bump up on the button at speed . Any more than that and you will be tossing a nice roost but loosing your bite on the water and with that...speed . You can not trim a cat like you would a v hull nor for safeties sake should you want to . I don't have the power you do and my porpoise starts at 82 mph , right where I run out of power . I added fixed tunnel tabs and it helped a little but I'm sure the only cure for me will be mo power so I can run past it . I'm curious if your 91' came with a stepped hull . Just wondering why your porpoise is so much farther up the speed scale . Here's a pic that show's a tab . They do make it easy to get back in the boat from the water .

dave269

Yes my 91 has the stepped hull, I bought it last year out of Virginia w/o a mtr. Does your engine mounts sit on aluminum spacers ? I was wondering if these are factory or someone raised the mtr & outdrive up. They are about 1.5" thick. Pm me and I'll send you some pics

the deep

iTrader: (8)

PM'd ya .

ChrisnLBC

I have a 2002 with a 496HO, so no where near as much power. I do get the porpoise between 65-75 (75 is Top Speed of Mine right now, 28 Pitch 4 Blade Bravo, 110 Degrees at Havasu 4800 RPM) if the water is completely flat. If its chopped and aired out, I never feel it. When its flat, the boat just hates it. Sometimes if I'm going slow setting into a turn, the boat starts venting, and "falling off" side to side. Its a weird feeling, but I haven't really pushed the edges on it yet either.

But when the water is right, and I have a nice head wind, the boat just says "Thank You Dad, lets rock!"

HiMark Racing